Illegal to use? I think you mean Novus is on the list of diploma mills however obviously that is not criminal or they would be prosecuted since they are not hard to find.It varies by state. And it is what it is.
I'll post a link as an example. Don't presume, its a dangerous thing.
Institutions Whose Degrees are Illegal to Use in Texas
Consonant with its responsibilities under Chapter 61 of the Texas Education Code and rules promulgated pursuant thereto, the Texas Higher Education Coordinating Board annually reviews the institutions included on this list.
"Fraudulent or substandard degree" means a degree conferred in Texas in violation of the Texas Education Code; conferred in another state in violation of that state's laws; conferred in another state by an institution that was not accredited by an accreditor recognized by the Coordinating Board and that has not been approved by the Coordinating Board for its degrees to be used in Texas; or conferred outside the United States by an institution that the Coordinating Board determines is not the equivalent of an accredited or authorized degree. (Texas Educational Code, Chapter 61, Section 61.302)
The Texas Penal Code (Section 32.52) prohibits the use of fraudulent or substandard degrees "in a written or oral advertisement or other promotion of a business; or with the intent to: obtain employment; obtain a license or certificate to practice a trade, profession, or occupation; obtain a promotion, a compensation or other benefit, or an increase in compensation or other benefit, in employment or in the practice of a trade, profession, or occupation; obtain admission to an educational program in this state; or gain a position in government with authority over another person, regardless of whether the actor receives compensation for the position." Violation of this law is a Class B misdemeanor.